As shown in Japanese Unexamined Patent Publication No. 118521/1990 (Tokukaihei 2-118521; published on May 2, 1990) for example, a conventional liquid crystal display device uses a technique such that: a color filter indicative white (W) is provided in addition to color filters indicative of red (R), green (G), and blue (B) so that the color filters constitute one block, and the color filters are pattern-arranged using the block as a unit, allowing luminance to be improved. In the liquid crystal display device, for example, white light is emitted from a backlight such as a fluorescent lamp, passes through a liquid crystal to change its transmittance, and passes through color filters indicative of red (R), green (G) and blue (B), so that a color image is recognized by human eyes. Light having passed through the color filters reduces a considerable amount of luminance. For that reason, by adding a color filter indicative of white to one block, it is possible to increase luminance of light emitted by one block.
Examples of a pattern arrangement for the sub-pixels indicative of red (R), green (G), blue (B), and white (W) include a matrix pattern arrangement in which the sub-pixels are arranged in a matrix pattern as shown in FIG. 15(a) and a stripe pattern arrangement in which the sub-pixels are arranged in a stripe pattern as shown in FIG. 15(b).
Assume that, in a conventional arrangement, one block, that is, one pixel allows three sub-pixels indicative of red (R), green (G), and blue (B) to output luminance corresponding to 1. In contrast, in the matrix pattern arrangement or the stripe pattern arrangement for four colors, one pixel allows three sub-pixels indicative of red (R), green (G), and blue (B) occupying ¾ of an area of the block to output luminance corresponding to ¾, and allows a sub-pixel of white occupying ¼ of the area to output luminance three times as large as the luminance outputted by the three sub-pixels. Consequently, total luminance outputted by the one pixel is (¾)×1+(¼)×3= 3/2. Therefore, as a whole, it is possible to make brightness of one pixel larger than that of one pixel in the conventional arrangement by 50%.
As shown in FIGS. 5(a) and 5(b) which are explanatory drawings of the present invention, each sub-pixel of a liquid crystal display panel includes a TFT (Thin Film Transistor) element 6. A drain of the TFT element 6 is connected with a pixel electrode 7 of each sub-pixel.
As shown in FIG. 6 which is an explanatory drawing of the present invention, a parasitic capacitance Cgd exists between a gate and the drain of the TFT element 6. Consequently, when the gate of the TFT element 6 is OFF, a pixel voltage is led in (a pixel voltage decreases) by ΔV due to the parasitic capacitance Cgd.
Therefore, as shown in FIG. 7 which is an explanatory drawing of the present invention, a voltage applied on the pixel electrode is lower than a written voltage (voltage supplied to a data signal line) by ΔV.
A liquid crystal must be driven with an alternative current and therefore a TFT liquid crystal display device adopts a frame-reversal drive scheme, a dot-reversal drive scheme, or other schemes. A voltage corresponding to a potential difference between a counter electrode voltage and a pixel electrode voltage is applied on a liquid crystal. However, a pixel electrode voltage is lower than a written voltage by ΔV both at a time of + polarity and at a time of − polarity, resulting in difference in an absolute value of a voltage applied on a liquid crystal layer 3 between the + polarity and the − polarity. Consequently, luminance differs between the time of + polarity and the time of − polarity. As a result, flickers are generated.
A conventional driving device for a display panel and a display device including the driving device are premised on even-numbered sub-pixels as shown in FIGS. 15(a) and 15(b). Consequently, in a stripe pattern arrangement in FIG. 15(b) for example, flickers are generated in which a stripe pattern is recognized in a lateral scanning direction when one color is displayed all over a screen. In a matrix pattern arrangement in FIG. 15(a), flickers are generated all over the screen.
See a sub-pixel indicative of red (R) for example in the matrix pattern arrangement. Assume that, in one frame, all sub-pixels indicative of red (R) have + polarity and an absolute value of a voltage applied on a liquid crystal is 3V for example due to a lead-in voltage, which is recognized as shown in FIG. 16(a).
On the other hand, assume that, in a next frame, all sub-pixels indicative of red (R) have − polarity and an absolute value of a voltage applied on the liquid crystal is 4V for example due to a lead-in voltage. Consequently, as shown in FIG. 16(a), red (R) is emphasized, and an image on a screen is recognized as reddish as a whole. As frames proceed, the display in FIG. 16(a) and the display in FIG. 16(b) are repeated alternatively, which is recognized by human eyes as flickers. The same can be said about other colors. For example, an image in a certain frame is recognized as bluish.
Polarity reversal drive control of a liquid crystal is disclosed in Japanese Unexamined Patent Publication No. 149117/2002 (Tokukai 2002-149117; published on May 24, 2002), Japanese Unexamined Patent Publication No. 83527/1990 (Tokukaihei 2-83527; published on Mar. 23, 1990), and Japanese Unexamined Patent Publication No. 94389/1989 (Tokukaihei 1-94389; published on Apr. 13, 1989). However, none of them discloses a relationship between the polarity reversal drive control of a liquid crystal and a pattern arrangement of color filters.
The present invention was made in view of the foregoing problems. An object of the present invention is to provide (i) a driving device for a display panel, (ii) a display panel, (iii) a display device including the driving device, and (iv) a method for driving the display panel, each of which allows for preventing flickers which are caused because color is emphasized or not in a whole screen.